Unknown JavaScript syntax before for…in

Question

I am reading a book about single-page applications and at some point there is this for...in loop:

KEYVAL:
for(key_name in arg_map){
    if(arg_map.hasOwnProp         


        

Answer 1

It is for break and continue.

Check the MDN

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label